State: Avoid URL redirect for published post autosave

[aduth]

Fixes #7066

This pull request seeks to resolve an issue where the editor URL is replaced with an autosave ID when autosaves occur for published posts. Since autosave posts are not directly editable, this results in an error message if the user proceeds to reload the page.

Implementation notes:

As part of some consolidation refactoring in #6257, I made assumptions about an autosave success result receiving a post object, which is only partly correct. In fact, the autosave endpoints return a subset of post properties. Notably, this does not include some properties like status, which is considered in both the effects handlers for post save success and failure, and would be undefined in the case of an autosave. Since these handlers seem to handle this gracefully, I did not address that as part of the changes here, but it seems fragile to allow this assumption to continue.

This change was intended to be the minimal fix to allow a 3.0 release to proceed, but I'd like to proceed with future refactorings of this behavior in subsequent pull requests, both:

• Moving the URL updating logic out of editor to edit-post
  • Related: Data Module: Add support for action creators as generators #6999 (comment)
• Updating the post URL in response to RESET_POST, which won't trigger on autosave, only full saves.

Testing instructions:

Repeat steps to reproduce from #7066, verifying that no error screen is presented, and that the browser URL does not change after an autosave occurs for a published post.

Ensure unit tests pass:

npm run test-unit ./editor/store/test/effects.js

[youknowriad]

Maybe it's not related to this PR but I'm not seeing the autosave prompt after refreshing the page?

[aduth]

@youknowriad That's expected. See also #4218, ##4112 (comment) . Maybe if release is by Monday we can see about getting #4218 in as well for a complete autosave experience.

[adamsilverstein]

👍 LGTM

[aduth]

Thanks for the review @adamsilverstein !